1. Field of the Invention
The invention relates to multifunctional lubricant additives for imparting antiwear and extreme pressure properties. In particular, the invention relates to novel hydroxyalkyldithiocarbamate borate esters and the process for preparing such compounds, as well as the precursor compounds and lubricating compositions containing such compounds.
2. Description of the Prior Art
The development of lubricants represents an important area of technology aimed at finding ways to reduce friction between contacted moving components in various mechanical devices. The mechanical wear of these components is greatly accelerated by friction, thus increasing the expense of operating mechanical devices.
A variety of additives are used in lubricants to substantially improve performance. For example, extreme pressure (EP) additives are routinely incorporated into an untreated lubricating composition (e.g., greases) to significantly improve performance. Extreme pressure additives are believed to produce a film on the surface of the metal which can both increase the load carrying capacity of the lubricant, and protects the metal surface under high load conditions from deterioration due to wear, welding, and abrasion.
Lead naphthenates and lead dialkyldithiocarbamates are frequently used as additives to improve the EP performance of greases. However, lead is a heavy metal which is considered “poisonous” in all forms. As an alternative, metal additives (such as antimony, zinc, and bismuth) have been used as a replacement for lead. However, these heavy metals still provide environmental concerns regarding the use. Accordingly, it has long been a goal in the art to develop non-metal lubricating materials to replace heavy metal additives while providing acceptable extreme pressure performance.
Ashless dithiocarbamates, such as 4,4′-methylene bis(dibutyl dithiocarbamate) (Trade mark VANLUBE® 7723 available from R.T. Vanderbilt Company, Inc.), are also well known for their antioxidant and extreme pressure properties in lubricants.
Borates and borate esters are well-known to exhibit antiwear and other properties in lubricant applications. U.S. Pat. No. 905,649 from Chapman describes the use of borax in a grease composition. U.S. Pat. No. 2,234,581 from Rosen describes lubricating oils and greases containing a boron-containing compound useful in lubricants. U.S. Pat. No. 3,185,644 from Knowles, et al., describes amine salts of borate esters that are useful as lubricant additives. U.S. Pat. Nos. 3,224,971 and 3,239,643, also attributed to Knowles, et al., describes novel borate esters and lubricant compositions thereof. More recently, U.S. Pat. No. 5,698,499 from Baranski, et. al., describes phenolic borates that are useful antiwear additives.
More recently, there have been reported multifunctional additives that combine both the antiwear capabilities of borates and borate esters with the extreme pressure and antioxidant properties found in ashless sulfur-containing compounds. U.S. Pat. Nos. 3,303,130, 5,885,943 and 6,028,210 describe the preparation of borate thioesters useful as antiwear additives and antioxidants. U.S. Pat. Nos. 5,126,063, 5,182,036, 5,370,806, and 5,698,498 describe the preparation of borated dithiocarbamate esters that are useful as antiwear, extreme pressure and antioxidant additives. These materials are prepared from dithiocarbamate salts and their reaction with and epoxide compound, followed by reaction with boric acid to form the borated dithiocarbamate ester. A borated dithiocarbamate is described by Chiu in U.S. Pat. No. 5,672,727.